TC4钛合金承重框双道双侧不等熔深EBW接头组织与性能研究

According to the structural characteristics of 140 mm thick hollowed-out load-bearing TC4 titanium alloy beam, a double-side and double-pass electron beam welding (EBW) scheme with unequal penetration was proposed. The welding test was carried out and the microstructure and properties of the obtained joint were analyzed. It is found that the microstructure of the weld zone is obviously non-uniform in the direction of thickness, and the overlapping zone at the root of the two welds is the most noteworthy part. There are a lot of needle α' phase and scattered β phase in the overlapping area of the root of the two welds, while the needle phase is short and the interlacing phenomenon of α' phase is obvious. The needle α' phase and α phase distributed in the original β grain boundary are observed in other weld areas of the joint, but the laths are longer and arranged in a more obvious direction. The microhardness of the weld in the overlap zone of the root of the two welds is about 10% higher than that of the other weld zones in the joint (3410~3460 MPa). At room temperature, the impact energy of the weld in the overlap zone at the root of the two welds is about 11% lower than that of the other weld zones in the joint (about 47 J). The area where the roots of the two welds overlap is the area where the joint have the lowest tensile strength. With the aid of finite element simulation, it is found that the cooling rate around 900 ℃ of the overlapping area of the root of the two welds is higher than that of the other areas of the welds, which is an important reason for the difference in the microstructure and performance between the overlapping area and the other areas of the welds. It is noted that all joints are broken in the base material area during tensile tests, and it is believed that the inhomogeneity of microstructure and properties of large-thickness forgings in the direction of thickness result in the inhomogeneity of tensile strength of joints. The results show that it is feasible to use double-side and double-pass unequal penetration EBW welding scheme to fabricate thick hollowed-out load-bearing TC4 titanium alloy beam. Meanwhile, some beneficial measures such as improving the uniformity of microstructure and property of the base material and strictly controlling the interval time between two passes of welding are recommended.